m = 3, n = 7

var uniquePaths = function (m, n) {
    let dp = new Array(m).fill(0).map(() => new Array(n).fill(0))
    // dp[i][j]  到达(i,j)位置时所有的路径
    // dp[i][j] = dp[i-1][j] +dp[i][j-1]
    for (let j = 0; j < n; j++) {
        dp[0][j] = 1
    }
    for (let i = 0; i < m; i++) {
        dp[i][0] = 1
    }
    for (let i = 1; i < m; i++) {
        for (let j = 1; j < n; j++) {
            dp[i][j] = dp[i - 1][j] + dp[i][j - 1]
        }
    }
    return dp[m - 1][n - 1]
};

console.log(uniquePaths(m, n));
